The invention relates to water-dilutable polyurethanes containing structural units derived from 3,4-epoxy-1-butene and also to aqueous dispersions comprising these polyurethanes, to a process for preparing them and to use as aqueous oxidatively drying and/or UV-crosslinking coating compositions.
Polymeric compounds which may comprise the structural units of 3,4-epoxy-1-butene are known in principle. EP-A 0 217 660, for example, describes the preparation of poly(xcex1-hydroxycarboxylic acid) copolymers using ethylenically unsaturated epoxides.
U.S. Pat. No. 5,393,867 discloses hydroxy-functional polyethers which are obtained by polymerizing 3,4-epoxy-1-butene with palladium catalysts.
EP-A 0 859 021 describes compounds which possess pendant vinyl groups and are prepared by reacting (a) compounds comprising at least one vinyl group and at least one epoxy group, (b) a polybasic compound or its anhydride, and if desired (c) a CH-acidic compound; their epoxidized derivatives are also described.
WO 00/66646 discloses oil-free oxidatively drying polyester resins which are obtained by derivatizing carboxyl-functional polyesters with 3,4-epoxy-1-butene and also discloses the use of these resins in combination with an organic solvent and a drying catalyst in coatings which dry at room temperature.
WO 00/66649, finally, discloses coating compositions based on polyether alcohols which are prepared by ring-opening polymerization of 3,4-epoxybutene with water or alcohols. The polyether alcohols thus prepared can be used as reactive diluents or binders in oxidatively drying coatings and also as a building block for such binders.
Disadvantages of the aqueous one-component coating materials known to date in coatings technology include the fact that, for example, the drying of oxidatively crosslinking waterborne coating materials at room temperature is often slow, even where siccatives are added as drying accelerators, and that only moderate film hardnesses are achieved. UV-curing aqueous one-component coating materials, on the other hand, exhibit insufficient crosslinking in areas which have been irradiated with a relatively low UV dose or not at all (shadow regions). The coating films in these areas have a low-grade level of properties.
It was an object of the present invention, accordingly, to provide aqueous dispersions which are capable of oxidative drying and/or crosslinking with UV light and which can be processed to give one-component coating materials having a high level of properties, especially with respect to film optical properties, hardness, solvent resistance, weather resistance, and rapid drying.
It has been possible to achieve this object by providing a water-dilutable polymer which contains urethane groups, which contains the structural units of 3,4-epoxy-1-butene, and which can be used as a basis for a one-component aqueous dispersion.
The present invention accordingly provides a water-dilutable polymer containing urethane groups and containing ionic and/or potentially ionic groups, characterized in that the polymer comprises the repeating units (A1) of the formula (I) and/or (A2) of the formula (II) 
The repeating units A1, A2 or A1/A2 mixtures in the polymer are in blocks 
or in blocks which are a mixture of both structural units, with p repeating units, where n, m and p each represent whole numbers from 3 to 100.
It is likewise possible for the A1 or A2 repeating units to be distributed differently in the copolymer.